Focusing on the requirements of quality, efficiency and process change, China's machinery manufacturing process equipment, mainly CNC equipment, has undergone profound changes at the technical level. The functions of CNC machine tools are continuously enriched, and the process, process concentration and compounding technology are adopted. The machine tools have new developments in structural layout and new material application; CNC technology is open, intelligent, networked, high-speed and high-precision. New developments have been made. The purpose is to improve production efficiency, improve accuracy, ensure quality and maximize benefits.
Constant pursuit of high quality and high efficiency is the eternal theme and goal of mechanical manufacturing research, and is the source of power to promote the development of its process equipment. Process requirements and changes are the basis and basis for the development and innovation of mechanical manufacturing process equipment technology.
Domestic CNC machine tools have gone through a long process of 50 years of development. In the past 10 years, they have achieved rapid development. In particular, they have received the attention of the government and set up major technical research projects to effectively promote the development of CNC machine tools.
At present, domestic CNC machine tools are available for more than 1,500 varieties, covering CNC metal cutting machine tools, CNC sheet metal working machines (CNC punching machines, CNC laser processing machines, flame cutting machines, etc.), CNC electric machine tools, industrial robots, and three-coordinates. Measuring machines, etc., the types are basically complete. In 2010, the number of CNC metal cutting machine tools was about 1.5 million units (including more than 400,000 units). The annual output of metal cutting machine tools exceeded 160,000 units. In 2011 and October, the total number reached 218,000 units. It can reach about 250,000 units. The number and value of domestic brand CNC machine tools account for more than 50% of the domestic market. New progress has also been made in the five-axis linkage and compound machining centers, numerical control systems and other supporting technology products that represent advanced technology. This article focuses on the development of CNC technology and the gap.
Pursuing high productivity
In order to pursue the high productivity of mechanical manufacturing, it promotes the development of CNC equipment to process compounding (process compounding and process compounding), high speed, intelligent, network, and process parameter optimization.
1 composite
CNC machine tool composite processing mainly refers to process concentration, compounding and process compounding.
1.1 Process concentration and compounding
Since the end of the 1970s, as the triple-link machining center began to be used in machinery manufacturing, it has entered the era of centralized machining processes. In the 1980s, China's self-made three-link machining center also began to be used in machinery manufacturing, mainly for box parts and mold processing. In one installation, multiple processes such as boring, milling, drilling, tapping, etc. can be realized, which improves processing efficiency and precision.
2000~2011 is the fastest period for the development of CNC machine tools in China. During this period, the company independently developed a five-axis linkage machining center, a turning and milling composite machining center, a turning and milling combined machining center, and a grinding compound machining center. Some domestic manufacturers have been able to provide five-axis linkage and multi-axis linkage composite machining centers, but some are major special projects, which are subject to further commercialization and industrialization.
1.1.1 Five-axis linkage machining center
The number of domestically produced five-axis linkage machining centers is increasing. Such as the GMC2590μ bridge five-axis linkage machining center produced by Shenyang Machine Tool (000410), VM22120μ vertical five-axis machining center, VMC05656e gate five-axis machining center, HS664RT five-axis high-speed machining center; VDM500 five-axis vertical generation produced by Dalian machine tool Machining Center; XKR32G 5-axis linkage machining center and XKH800 5-axis linkage blade machining center produced by Beijing Electromechanical Institute; XV2525×60 overhead 5-axis linkage machining center produced by Jinan No. 2 Machine Tool can realize milling and boring of one-time installation parts , drilling, reaming, tapping and other processes.
It is technically difficult to develop two key core components in a five-axis linkage machining center. One is a double-angle universal machining head; the other is a two-axis rotary table (see Figure 2). Domestic manufacturers of these two components have also been developed, but they need further improvement and commercialization. The double swing angle universal machining head is used for large machine tools, and the double swing shaft rotary table is used for small machine tools. Currently, these two components use direct drive torque motors and are equipped with encoders to improve dynamic performance and accuracy.
The double swing angle universal machining head is more technically difficult. The main parameters of a direct drive double swing angle universal head developed by a domestic manufacturer are as follows:
The amount of torque: A-axis 500~1000Nm (optional), C-axis 660~2000Nm (optional);
Positioning accuracy: ±2", ±2.5", ±3", ±5" (optional);
Absolute encoder resolution: 26 bits, 29 bits (optional);
The swing angle range is ±110° for the A-axis and ±360° for the C-axis.
China has not yet formed a series of products with double swing angles, but internationally, like CYTEC in Germany, it can supply serialized products.
1.1.2 Turning and Milling Compound Machining Center
The turning and milling combined machining center has been developed on the basis of CNC lathes and also developed on the basis of vertical machining centers. For example, the CK1840S type turning and milling composite machining center produced by Nanjing CNC Machine Tool Co., Ltd. was developed on the basis of CNC lathe. The machine has two spindles, two tool holders, two C-axis and W-axis, a total of seven axes, divided into two groups of three-link full-closed control. The C-axis resolution is 0.001°. The machine tool can complete turning, indexing eccentric drilling, positioning milling and other processes in one loading of the rotary parts, that is, one turning and milling machining center can complete the processing steps of two CNC lathes, and the efficiency is doubled. Accuracy is improved by reducing secondary mounting errors. The CX110 vertical turning and milling composite machining center produced by Anyang Xinsheng Machine Tool Co., Ltd. was developed by adding turning equipment to the vertical machining center. The machine has the functions of car, boring, milling, drilling, reaming, tapping, etc. It can realize five-sided machining of five-axis linkage. In addition, the VHT800 five-axis linkage turning and milling composite machining center developed by Dalian Machine Tool, the CHD25 five-axis linkage turning and milling composite machining center, and the WHGS7000 turning and milling composite machining center developed by Wuhan Heavy Machine Tool Group Co., Ltd. Multi-process processing of complex structures and complex profile parts.
1.1.3 Car Milling and Grinding Compound Machining Center
The HTM-V120L CNC vertical car milling and grinding combined machining center developed by Ningbo Haitian Seiko (601882) Machinery Co., Ltd. can complete the multi-step process of turning, milling and grinding with one workpiece, and can also carry out heavy cutting high-precision machining. For large bearing processing.
1.1.4 Turning and Milling Gear Processing Compound Center
Some turning centers have a second spindle and a grinding wheel shaft mounted on the rotary tool holder. On the second spindle, gear tools can also be installed to machine the shaft gear and the worm wheel. Even five-axis linkage can be realized, and the arc gear and bevel gear can be processed by the finger milling cutter.
1.1.5 Grinding Composite Machining Center
The H405-BE CNC compound grinding machine developed by Shanghai Machine Tool Works Co., Ltd. uses SIEMENS numerical control system to control the grinding wheel frame and table feed respectively, the head frame spindle rotation and the grinding wheel frame rotation, with external grinding and automatic positioning of the grinding wheel frame, etc. Features. Automatic cycle grinding of inner and outer circles and end faces can be done in one loading.
1.2 Process Compound
Process compound processing is still rare in China. VTM3501 vertical car milling and laser quenching composite machining center developed by Shenyang Machine Tool Group SCHIESS. It can realize machining such as car, boring, drilling, tapping, milling, grinding and laser quenching. The machine combines a cold working process with a hot working process to greatly increase production efficiency.
According to the relevant data, a five-axis simultaneous machining center or multi-process composite machining center can increase production efficiency by more than one time compared with the triple-link machining center. Multi-axis linkage and composite machining not only improve production efficiency, but also reduce secondary installation errors and improve accuracy and quality. The domestic five-axis linkage machining center and multi-axis linkage composite machining center can be produced in China, but some of the major research products still need further commercialization and industrialization.
2 high speed
In order to achieve high-speed CNC machining, the drive system uses direct drive technology, and the CNC system uses high-speed arithmetic processing technology.
2.1 Direct drive technology
In order to improve production efficiency, CNC machine tool transmission parts gradually adopt direct drive technology. The main shaft adopts electric spindle direct drive, the feed is driven by linear motor, the rotary table adopts direct torque drive, and the five-axis linkage swing angle universal head adopts torque motor direct drive.
As early as 2000, China began research and development of direct drive technology. At present, Shandong Bote Precision Co., Ltd. and Luoxuan Research Technology (002046) Co., Ltd. can produce and supply electric spindle series products. Beijing Shouke Kaiqi Electric Technology Co., Ltd. has also developed linear motors. Users have responded well to the above product performance and technical indicators, but there is still a gap compared with the advanced level of foreign countries.
At present, the foreign advanced electric spindle unit speed can reach 15000~100000r/min, and the general use is more than 40,000~50000r/min. Feeding parts that use direct drive with a linear motor require both high speed and high acceleration and deceleration. The fast moving speed can reach 60~200m/min, the acceleration can reach 2g~10g; the working feed can be up to 60m/min and the acceleration can reach 1g~2g. The feed rate of the feed member using the conventional ball screw drive is 20 to 30 m/min, and the acceleration is 0.1 g to 0.3 g; in general, the feed speed is about 30 m/min. The direct drive is more than doubled in feed rate than the ball screw drive, which reduces auxiliary time and increases productivity. Linear motor drive technology has broad application prospects, but it is necessary to further reduce costs and solve heat problems.
At present, direct-drive technology has been adopted in CNC machine tools developed by some manufacturers in China. For example, the XHV2525×60 overhead five-axis linkage high-speed boring and milling machining center developed by Jinan No. 2 Machine Tool uses linear motor drive for the x and y axes. The two rotary axes of the XKR32G five-axis linkage machining center table developed by Beijing Electromechanical Institute adopt direct torque motor drive, and the main shaft of XKH800 five-axis linkage blade machining center adopts electric spindle direct drive. The direct drive technology of domestic CNC machine tools is still in its infancy, and it is still not widespread. There is still a certain gap in performance. More than 1,500 CNC machine tools produced by DMG in Germany use direct drive technology. The FZ12KS five-axis machining center produced by Germany Julang Company has a spindle speed of 40,000r/min, a tool change time of less than 0.6s, a feed acceleration of 1g~2g, a rapid feed rate of up to 90m/min, and a workpiece exchange time of 2s. .
2.2 CNC system high-speed arithmetic processing technology
The high-speed direct drive feed requires the CNC system to have a fast calculation speed, a short sampling period, and sufficient advance path plus (decrease) speed to optimize the block preprocessing capability. More advanced CNC systems can preprocess thousands and tens of thousands of blocks. In the multi-axis linkage control, the acceleration/deceleration optimization processing can be performed according to the G code of the pre-processing buffer. In order to ensure the processing speed, the sixth generation CNC system can change the feed rate by 2000~10000 times per second.
3 intelligent
In order to pursue the processing efficiency and processing quality of CNC machine tools, the CNC system not only has automatic functions such as automatic programming, feedforward control, fuzzy control, self-learning control, automatic generation of process parameters, 3D tool compensation, motion parameter dynamic compensation, etc., and has fault diagnosis. The expert system makes the self-diagnosis and fault monitoring functions more perfect. The servo drive system is intelligent, can automatically sense load changes, and automatically optimize adjustment parameters.
The domestic CNC system is working hard towards the development of intelligence and introducing some intelligent technologies. For example, the “China 8†and the Kanedi K1000TIV in Huazhong, etc., all have intelligent functions such as self-diagnosis function, real-time display of status and real-time alarm of faults, and are further enriching and perfecting intelligent technology.
The intelligent technology integrated into the CNC system produced by Siemens, FANUC and Mitsubishi is more abundant. There are still many gaps in the domestic CNC system. For example, SINUMERIK 828DBASICM from Siemens has the intelligent coordinate transformation function for cylindrical parts machining. It has the SINUMERIKMDynamics technology package and contains all the “fine surface†functions for efficient machining and optimum surface quality. Fanuc's Oi-D and OiDMate have contoured intelligent control functions, and the 30i/31i/32i/35i-MODELB series CNC system is the latest artificial intelligence nano-scale system, which can flexibly support boring and milling machining centers and CNC lathes. Linkage combined machining machines, etc. Intelligent technology has a great contribution to improving the production efficiency of CNC machine tools, and must be taken seriously.
4 open and networked
The openness of the numerical control device can more easily realize intelligent networked manufacturing and effectively promote the improvement of production efficiency.
4.1 Open
Open CNC means that the hardware, software and bus are open to the user. The main advantage of the open CNC device is that it has better versatility, flexibility, adaptability and scalability, which can meet the requirements of secondary development of users.
4.1.1 NC and CNC concepts and openness
At present, there are two types of numerical control devices, NC and CNC. A numerical control device composed of hardware logic circuits is called an NC device; a numerical control device composed of computer hardware and software is called a CNC numerical control device. Hardware is the physical basis for software operation, and software is the soul of the entire CNC operation and function implementation. The NC is gradually being replaced by the CNC.
In addition to the CPU, EPROM, and RAM, the CNC device hardware also has a position controller, a manual input (MDA) interface, a display (CRT) interface, and a PLC interface. Therefore, the CNC numerical control device is a
Dedicated computer.
CNC software is divided into two types: management software and control software. Management software is used to manage the input and output of part programs, tool position system parameters, part program display, machine status fault diagnosis and alarms. The control software consists of software such as decoding, interpolation, calculation, tool compensation, speed control, and position control.
The modern open CNC device is mainly a CNC numerical control device developed on a PC platform. China's "Huazhong 8" CNC device adopts an open hardware and software architecture based on multi-processor and independent innovation bus technology. The hardware crosses the platform, the software can be replaced, and the software and hardware have multiple levels of open functions. Beijing Kanedi's K1000TIV numerical control device adopts an open PLC and provides debugging software to support users' secondary development. Guangzhou CNC's GSK25i CNC device also uses an open PLC to support PLC ladder diagram online editing, diagnosis and signal tracking.
4.1.2 Standards and Specifications
Whether the openness of numerical control devices can be realized is closely related to the establishment of technical standards and norms. For more than 50 years since the birth of CNC technology, information exchange has been based on the ISO6983 standard, which uses G and M codes to describe how to process. Obviously, this standard is increasingly unable to meet the requirements of the rapid development of modern CNC technology.
In the 1990s, countries such as Europe, America, and Japan began to study and develop the architectural specifications for open CNC devices (OMAC, OSACA, OSEC), and developed open CNC devices as a development strategy. In 2000, China began to study and develop a standard framework for open CNC devices, but it is still not perfect.
4.2 Networking
Networking facilitates information sharing and productivity. According to the data, in the multi-variety and small-batch production, the time for cutting a CNC machine tool is only 25%~35% of the maneuver time, and after connecting to the network, it can be increased to 60%~65%.
CNC network technology, mainly the index control system and other external control systems or host computer network connection and network control. The CNC system is first oriented to the internal LAN of the enterprise and then transmitted to the outside of the enterprise via the Internet. This is called Internet/Intranet. The network enables cross-regional collaborative design, collaborative manufacturing, information sharing, remote monitoring, Remote Diagnosis and service between enterprises and enterprises. The network can provide complete production data information for manufacturing. The machining program can be transmitted to a remote machine tool through the network for processing, and remote diagnosis and command adjustment can be made. The network connects scattered CNC machine tools around the world, coordinates with each other, and unifies and optimizes the adjustment, so that product processing is not limited to one factory and realizes social production.
The development of information integration in China's machinery manufacturing enterprises is also relatively fast, achieving the integration of shop-level and enterprise-level information networks. The network development of CNC is promising, but there is still a long way to go to truly realize the information network across enterprises and regions.
5 optimize process parameters to improve efficiency
Whether the process parameters used in NC machining are reasonable is very important for improving production efficiency and ensuring processing quality, and it is necessary to gradually optimize and establish a process database.
There are two ways to optimize process parameters. One is to select reasonable process parameters through actual trial cutting, which is time-consuming, laborious, and costly; the other method is to apply dynamic optimization simulation method, which is less time-consuming, labor-saving, and material-saving than the first method. Reasonable process parameters. These parameters can also be reasonably adjusted in production practice.
The aviation industry is a large user of CNC machine tools, and there is an urgent need to optimize process parameters, build process databases, and apply them to production practices. Therefore, the government support organization Beijing University of Aeronautics and Astronautics and AVIC Beijing Aviation Manufacturing Engineering Research Institute carried out optimization of process parameters technology. The above units developed a complete set of process dynamics dynamic simulation, prediction and digital software and hardware systems, established a database of optimized process parameters, formed a manual for optimizing high-speed cutting process parameters, and fundamentally realized the selection of process parameters from trial cutting to simulation. Leapfrogging improves processing efficiency and quality. This is a significant and far-reaching job.
Shaanxi Aircraft Manufacturing Company applied optimized process parameters in nearly 100 parts processing, and the average processing efficiency increased by more than 2 times. Wangjiang Industrial Co., Ltd. adopted optimized process parameters in the processing of artillery parts, and the efficiency increased by more than 4 times; Changhe The Aircraft Industry (Group) Company processed aluminum alloy parts with optimized process parameters, and the efficiency was improved by 2.8 times or more.
The Siemens 828D CNC system features Dynamic Process Pack (Dynmics) with a new “Excellent Surface†feature for efficient machining and optimum surface quality.
China's CNC equipment manufacturers should also provide technology and services in this area. The use of process optimization parameters can not only improve production efficiency and improve processing quality, but also have important significance for material saving, energy saving and emission reduction, and green manufacturing.
Pursuit of high precision and high quality
Pursuit of high precision and high quality of CNC machined workpieces. First of all, the CNC machine itself must have such performance. For this reason, in the structure and layout of CNC machine tools, the rigidity and load carrying capacity must be considered in the material selection to ensure high precision; at the same time, the numerical control system, servo drive system, transmission system and measuring sensor must also have high resolution. High-precision performance can meet the requirements of high precision and high quality of workpieces.
1 structure layout
In order to achieve functions and improve rigidity, CNC lathes, turning centers, vertical machining centers, horizontal machining centers, gantry machining centers, and turning and milling composite machining centers have undergone profound changes in structural layout.
For example, vertical machining centers and horizontal machining centers produced by some domestic manufacturers use horizontal columns to move the columns. This reduces the number of work platforms (the traditional structure is a double-layer cross table), which improves the rigidity and load carrying capacity of the table. The gantry machining center develops from the stationary table and the double column to the bridge structure, that is, the workbench is fixed, and the two columns are made into a fixed wall. The guide rail is mounted on the wall, and the beam is longitudinally moved on the guide rail. This structure reduces the mass and motion inertia of the moving parts, facilitates quasi-positioning and reduces floor space.
The GMC2590μ bridge five-axis machining center produced by Shenyang Machine Tool, the XHV2525×60 overhead five-axis linkage high-speed boring and milling machining center produced by Jinan No. 2 Machine Tool, and the trans-rail high-speed gantry machining center produced by Taiwan Asia Pacific Elite (share) Co., Ltd. A bridge type gantry frame structure is adopted. The structure has reasonable layout, good rigidity, strong carrying capacity, uniform force, good heat balance, stable precision and small floor space. The typical structure layout is shown in Figure 3.
2 using new materials to increase rigidity
The development and application of high-quality new materials for CNC machine tools is very important to improve the overall rigidity and precision of CNC machine tools.
For example, Ningbo Haitian Precision Machinery Co., Ltd. uses a 90% granite component polymerized cast bed on the HTM-V120L CNC vertical car milling and machining center. According to the factory, the bed made of this material is 10 times more shock-resistant than the cast iron bed.
For example, Dalian Kede Company uses artificial stone in the base of the TG-45 six-axis (or five-axis) linkage CNC tool grinding machine.
It is said that the above two companies have applied these two new materials, because of their shock absorption, stability and wear resistance, it provides a guarantee for improving and maintaining the accuracy of the machine.
In addition, there are also data showing that honeycomb materials, cement materials, natural granite stone, etc. are also used in numerical control equipment. Emphasis on the development and application of new materials will inevitably lead to changes in the design and performance of machine tools.
3 high precision interpolation CNC system
The application of high-digit CPU (64-bit) on numerical control devices, high-speed nano-level interpolation operation, high-resolution servo and other functions make an important contribution to improve the accuracy of CNC machine tools.
The CPU applied to CNC machine tools has grown from 16 bits in the 1980s to 64 bits now, and its frequency has increased from 5 MHz to 10 MHz to thousands of MHZ. The development of the CPU further increases the operation speed and resolution (0.1 μm, 0.01 μm). The domestic CNC system began to adopt 64-bit CPU, which can realize micro-scale precision interpolation, but there is still a distance compared with foreign advanced CNC systems.
For example, the FANUC 30i/31i/32i/35iB series CNC system, the Mitsubishi M700V CNC system, and the Siemens 828D CNC system are all nano-scale interpolation or nano-level operation precision.
Achieving nanoscale precision interpolation, servo drive system control resolution and responsiveness is critical. For this purpose, a high-precision sensor (16×106 lines/rev) is mounted on the servo motor shaft in the drive unit, and a high-resolution (1 μm) grating scale is used in the closed-loop system to make the positioning accuracy of the moving parts of the small CNC machine tool. It reaches 2~3μm. Under normal circumstances, domestic small CNC machine tools still can not reach this level.
Conclusion
Only the various components (including hardware and software) that make up the CNC equipment are excellent in technology, and the overall comprehensive performance can be excellent, in order to achieve high productivity, high precision and high quality. Moreover, each component has the function of ensuring production efficiency and quality, but the contribution rate is different. This article only introduces several important aspects of the development of CNC technology, which is not comprehensive enough.
It is important to emphasize that in the future, special attention should be paid to the research and innovation of new processes to promote the innovation of CNC products; special attention should be paid to the optimization of CNC process parameters and the establishment of databases to improve production efficiency and processing quality. It is necessary to pay special attention to the research and application of new materials to improve the performance of CNC machine tools; it is necessary to pay special attention to the development and application of intelligent network technology of numerical control technology, which has broad prospects.
The four special emphasiss above, the government should strongly support, CNC equipment manufacturers and machinery manufacturing enterprises should pay special attention to, and work tirelessly to make China's CNC machine tool technology development from follow-up to lead.
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